Stop auto-sending from Application

The send response listeners are now available to send the response
and handle requests more flexible.
Public sites should allow robots by default
Move robots.txt to robots.txt.dist

Staging sites should have a Disallow statement in the robots.txt,
so it should be configurable per installation.
Add Host and Sitemap directive for the robots.txt

The Host statement lets search engines understand which host should
be preferred (e.g. with or without www).

The Sitemap statement points search engines to a default sitemap where
all pages of this site can be found.
Merge pull request #4 from Soflomo/feature/public-cleanup

Feature/public cleanup